1. Field of the Invention
This invention relates to a keyboard for an input device, more particular to a keyboard with backlighting functionality that can be used in a notebook computer, a mobile phone, and the like.
2. Description of the Related Art
In order to use a notebook computer or a mobile phone at night or in a dark place, keyboards with backlighting functionality are commonly utilized. Such keyboards with backlighting functionality are disclosed in, for example, Taiwan patent Nos. 226621 and 223751, and Taiwan utility model Nos. M306689 and M330513.
A keyboard with backlighting functionality is a keyboard illuminated by a backlighting sheet. Usually, the backlighting sheet is a plate that allows light from light-emitting elements to propagate therein.
For example, a conventional keyboard with backlighting functionality disclosed in Taiwan patent no. M330513 comprises: a light-transmissive membrane circuit substrate; a keyboard base for supporting on underside of the membrane circuit substrate; a press key set having a plurality of press keys that are disposed on the membrane circuit substrate and that are capable of being pressed so as to cause the membrane circuit substrate to transmit input signals; a plurality of light-emitting elements disposed at one side of the membrane circuit substrate; and a light-guiding plate disposed under the keyboard base. The light-guiding plate has a backlighting sheet which allows light from the light-emitting elements to diffuse and to propagate therein, and a reflecting plate which is fixed under the backlighting sheet, and which is capable of reflecting light that exits from the backlighting sheet back thereto.
Since the top of each press key is made of a light-transmissive material, and since positions on the keyboard base corresponding to the press keys are also light-transmissible, the keyboard is capable of being illuminated by the light-guiding plate via the light-transmissive portions on the keyboard base and the top of each press key.
However, such a light-guiding plate, especially a backlighting sheet with a reflecting plate, would undesirably increase the overall thickness of the keyboard. Thus, a keyboard with such light-guiding plate cannot meet the current trend towards minimizing thickness.
Furthermore, in the prior art example, even if the conventional keyboard with backlighting functionality includes the reflecting plate, the light diffused in the light-guiding plate will be indiscriminately reflected toward the press keys by the reflecting plate based on the incident angle of the light. Apparently, the light is not concentrated but is reflected toward a broad range of the press keys, and thus, a larger number of the light-emitting elements becomes necessary. Particularly, when the keyboard is produced in a larger size, it is necessary to dispose more light-emitting elements in the keyboard, and thus, the manufacturing cost is accordingly increased. Besides, in the conventional keyboard with backlighting functionality, the brightness of the tops of the press keys depends on the distance between the press keys and the light-emitting elements, and thus, the tops of the press keys are likely to have a weakened brightness if their distances from the light-emitting elements are relatively far.